Products and methods relating to transverse thermoelectric materials and devices are disclosed herein.
Some known longitudinal thermoelectric devices include extrinsically doped p- or n-type materials. Electric current can be applied to these longitudinal thermoelectric devices in order to cause heat to flow along the same axis as the electrical current (e.g., parallel or anti-parallel to the current flow) throughout the entirety of the longitudinal thermoelectric devices.
The use of such longitudinal thermoelectric devices may be restricted since the dopants in semiconductor materials of the devices may freeze out at relatively low temperatures. For example, the dopants may fail to ionize or produce charge carriers (e.g., electrons and/or holes) for conduction in the semiconductor materials at relatively low temperatures.
Additionally, the efficiency of these devices in cooling objects may be limited. For example, in order to achieve sufficient cooling of a target object, both n-type and p-type longitudinal thermoelectric materials may be required for each device, and a cascade of multiple devices in parallel and in series may be needed to achieve large temperature differences. The required use of several pieces of such materials for each device, and of several devices in cascaded layers to achieve large thermal differences can limit the use and/or efficacy of the devices in cooling objects that are in relatively small or tight locations, such as in computing devices.
Some known transverse thermoelectric devices include Nernst-Ettinghausen effect (N-E) devices and Stacked-Synthetic (S-S) devices. In N-E devices, an external magnetic field is applied to a semimetal in order to cause heat flow along an axis that is transverse to the electrical current.
One disadvantage of some known N-E devices is the need to apply a large, uniform magnetic field. This makes the use of such devices impractical in most applications due to the need to surround such devices with a large electromagnet. Moreover, the transverse thermoelectric effect in such devices may be too small to compete with longitudinal thermoelectric effect devices at room temperature. Therefore, such devices are only employed at low temperatures (e.g., 100 K-150 K), and where the application can tolerate a large external electromagnet (e.g, 1.5 T).
In some known S-S devices, millimeter sized slabs of extrinsically-doped semiconductor having a large Seebeck coefficient are alternated with a slabs of metals (or semimetals) having large electrical and thermal conductivity. When an electrical current is applied to such devices, heat flows along an axis that is transverse to the applied current.
Disadvantages of S-S devices include a limitation that the devices may only be manufactured on a macroscopic scale, and the devices can be limited to only perform at temperatures where standard longitudinal thermoelectrics already provide superior performance. Because S-S devices are made of millimeter-thick slabs, the devices may need to be of the scale of centimeters or larger. It may be too technically challenging and labor intensive to thin such slabs and then assemble the slabs to try to manufacture a sub-millimeter scale device, and no known attempt appears to have been made thus far. Thus, such materials may be restricted to macroscopic devices. Since one of the layers is an extrinsically doped semiconductor, however, S-S devices may lose functionality at the same temperatures as macroscopic longitudinal thermoelectrics. For at least this reason, some known S-S devices have not offered a significant useful performance advantage over longitudinal thermoelectric devices, and have remained a laboratory curiosity.